Heat of Formation of O2−

Abstract

A series of Born–Mayer‐type calculations are used to calculate the lattice energies of simple oxides (MgO, BeO, CaO, and ZnO). Repulsion and other non‐Coulombic contributions to the lattice energy are obtained using thermodynamic and recent ultrasonic data for the bulk moduli and the isothermal pressure and temperature derivatives of the elastic constants. Using thermochemical data for the heat of formation of MgO, CaO, and BeO and their cations, the heat of formation of O²⁻, ${\mathrm{\Delta H}}_f\mathrm{°(}{\mathrm{O}}^{\text{2−}})$ , is calculated to be 197 ± 5 kcal/mole. Using the largest value of ${\mathrm{\Delta H}}_f\mathrm{°(}{\mathrm{O}}^{\text{2−}})$ , obtained for MgO, presumably the most ionic of the crystals treated, a value of 202.3 kcal/mole is obtained. These values are believed to be more accurate than earlier values given by Morris and by Huggins and Sakamoto who obtained 210 ± 6 and 221 ± 15 kcal/mole. The anomalously low value calculated for ${\mathrm{\Delta H}}_f\mathrm{°(}{\mathrm{O}}^{\text{2−}})$ for ZnO is believed to result from a substantial covalent contribution in the Zn–O bond in this oxide.